Thermal insulation suitable for vacuum bottles and the like



Dec. 12,1967, J. WE|SHAUPT 3,357,587,

THERMAL INSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov.12., 1965 5 Shets-Shee 1 7m Q v O I O O O 15: 15b A A Fig.2

lnvenfor 0 0551 WE/SHAUPT Dec. 12,1967 J, WEISHAUPT 3,357,587

THERIIIAL INSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov.127} 1965 s Sheets-Sheet 2 7/ 7/ I I j/ "'4 'llnmetalhzed- O. Layer w:

4 Metallized 0'1 1/ Layer Q llnmetallize'd layer Metallized layer 7 /NVENTOR,

JO SEF WEISHAUPT I ATTORNEYS Dec. 12, 1967 J. WEISHAUPT THERMALINSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov. 1965 3Sheets-Sheet 5 Fig. 3a

Layer INVENTOQ a055 .WE/5HA UPT A T QNEVS United States Patent 34Claims. 61420-4 This is a continuation-in-part application ofapplication Ser. No. 247,393,filed Dec. 26, 1962, claiming priority ofGerman application G 33,943 VIb/ 80b, filed Jan. 4, 1962.

This invention relates to insulation, particularly thermal insulation,and even more particularly to insulation which is highly useful in themanufacture of vacuum bottles and the like.

In the manfacture of liquefied gases such as hydrogen and helium, it isconventional to utilize storage containers which are essentially vacuumbottles, that is, there is an outer jacket afiixed to these containers,and a vacuum is maintained therein. The vacuum functions to eliminatethe transfer of heat by convection, and to a large extent by conduction;however, it is necessary to provide additional insulation for theprevention of heat transfer by radiation. It is thus well known that forsmall glass containers, a silver mirror is conventionally employed, butfor larger metallic containers, it is necessary to employ specialinsulation inside the evacuated jacket.

One type of insulation for this purpose consists of a mixture ofpowdered metal and non-metallic insulating material. This type ofinsulation, however, is disadvantageous because it is difiicult toevacuate, is likely to stratify, and is difiicult to repair. To overcomesome of these disadvantages, it would be possible to fabricate theinsulation from alternate metallic and non-metallic materials, but evenso, the final product would nevertheless be difiicult to evacuate, andadditionally, would not exhibit maximum thermal insulation becausebetween the metallic reflective layers, there would exist the poorlyreflective non-metallic foil.

The object of this invention, therefore, is to provide an improvedthermal insulation which is particularly suitable for the manufacture ofvacuum bottles and the like, and which, to a large degree, avoids thedisadvantages of the prior art materials.

Another object of this invention is to provide a process for thefabrication of the novel insulating material of the present invention.

Upon further study of the specification and appended claims, otherobjects and advantages of this invention will become apparent.

Briefly, the improvement provided by the present invention entails thedeposition of a metallic coating on a non-metallic, preferablyair-permeable, film, as will be seen from the accompanying drawings,wherein:

FIGURE 1 is a cross-sectional view of a vacuum bottle containing theinsulation of the present invention;

FIGURE 2 is a schematic diagram of a process for th fabrication of theinsulation of the present invention; and

FIGURE 3 is a magnified drawing of the insulation, FIGURE 3a being amagnified portion thereof, showing the interrelationship of theradiation reflecting surfaces.

The non-metallic base is any conventional thermal insulating materialwhich can be fabricated in the form of a film having a thickness ofabout 0.005 to 2.0 mm., preferably about 0.3 mm. suitable examples ofsatisfactory materials include mica, plastic films (e.g., polyadipamideof hexamethylene diamine, other polyamides, polyterephthalates, andpolyacrylonitrile), cellulose derivatives, such as cellulose triacetate,and conventional paper.

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It is preferred, moreover, to employ air-permeable films so that theycan be evacuated without much difiiculty. Non-woven materials made bythe conventional papermaking process are particularly suitable, forexample, fiberglass paper, and papers made of polyacrylonitrile,polyterephthalate, or polyamide fibers.

In addition to non-Woven fabrics or papers, it is also possible toemploy woven materials made of fibers of polyamide, polyterephthalate,and polyacrylonitrile. Among the woven materials, woven fiberglass isespecially suitable for insulating purposes.

These air-permeable base films in contrast to homogeneous films ofplastics or rubbers, exhibit high porosities. For example, the porosity,i.e., the proportion of the total volume of the films occupied by pores,is about 88- 98%, preferably 94%. The average pore diameter in a layerconsising of two fiber layers is about 0001-001 mm., preferably about0.004 mm. These two fiber layers are to be considered as a filmconsisting of fiberglass paper having a thickness of about twice thediameter of a single fiber. It is thus estimated that the number ofholes per mm. is on the order of about 1.5.10 The average pore diametersmay, of course,.vary according to the thickness of the films.Consequently they may, therefore, lie also beyond the given ranges.

The most preferred base material is fiberglass paper having a thicknessof about 0.0052 mm., preferably 0.1 to 2 mm., most preferably about 0.3mm., wherein the individual fibers of the paper have a diameter in therange of 0.3-1040- mm., preferably about 0.6- 10- mm. This fiberglasspaper is also advantageous because it is noncombustible and exhibitshigh mechanical strength.

The non-metallic base is coated with a metallic layer on one or bothsides. It is desirable to employ coatings of metals having a lowemission (less than about 5%), but a high reflection (not less thanabout 95%), such as gold, silver, copper, or aluminum, and alloysthereof which yield the desired properties, the preferred metals beingaluminum and silver. The metallic layer should be of sufficientthickness so that it will effectively stop even infrared rays, thisthickness being about 0.01-O.2'10 mm., preferably about 0.025-10- mm.,or on the order of about 10* mm. Of course, heavier layers of themetallic coating can be applied, but this would be undesirable from theeconomic standpoint; and if too thick a layer Were applied to porousmaterials, then of course there would be the danger of making the finalproduct nonporous.

One preferred embodiment of this invention is a multiple layerconstruction wherein a plurality of metallized films are superimposedover each other, it being particularly desirable to employ at leastfilms. Another preferred embodiment is a sandwich-type insulationwherein one or several (preferably about 50) metallized films and one orseveral non-metallized films are superimposed alternately, one over theother. The function of the nonmetallized base in the sandwichconstruction is to provide an additional barrier against heat transferby conduction.

The metallic coating can be deposited by any of several methods. Onesuch method is to deposit the metallic layer by immersing thenon-metallic base in a solution of a salt of a metal, or by spraying itwith such a solution. The coated base is then passed into a reducingsolution in order to precipitate the metal in situ on the base. Anotherpossibility is to deposit the metal from a suspension thereof in asolvent, for example, a colloidal suspension. The solvent is thenevaporated to dryness. Still another method involves vapor deposition ofthe metal.

If the base material is fabricated from fibers, either woven ornon-woven, it is also possible to coat the individual fibers with metalbefore the film is formed,

The final insulation of this invention has important advantages. Thehighly subdivided reflecting surfaces with point-like contacts betweenparticles result in low thermal conductivity. Since the spacing betweenmetallized fibers is much smaller than the usual spacing of films ofknown heat insulating materials, the temperature difference betweenadjacent reflecting surfaces and hence also the heat transmission willbe appreciably smaller.

These insulating materials can also be fitted more readily to curvedsurfaces; thus, there is assured a more uniform insulation over largesurfaces. Additionally, the manufacture and use thereof are generallysimplified.

For attaching the insulation to the inner wall of the vacuum jacket, itis possible .to use such expedients as wire bands, or nets of wire orplastic or textile fibers, the latter being preferred because of theirlow thermal conductivity. For maintaining or improving the vacuum insidesuch a filled insulation, it is preferred to incorporate an adsorbent inor under the insulation, examples of adsorbents being silica gel, activecharcoal, and molecular sieves.

The insulating material of this invention is useful not only for theinsulation of containers, but also as generaluse thermal insulation,particularly for low temperature equipment, e.g., for the insulation oflow temperature components of hydrogen and helium liquefying apparatus,and for the insulation of measuring means. Thus, it is obvious that itis useful for any apparatus provided with a vacuum insulating space.

Referring now to the drawings, FIGURE 1 shows a thermally insulatedcontainer for liquid hydrogen or helium which has been insulated withthe material of this invention. The primary container 1 is preferablymade of copper, or aluminum, or tombac (copper-base zinc alloy), or V2A(austenitic steel containing 18% Cr and 8% Ni). Tube 2 is used forfilling and emptying the container. Reference numeral 3 is the vacuumjacket, 4 is a tube for evacuating, and 5 is a partial and highlymagnified representation of the insulation of this invention. Elements 3and 1 thus represent spaced-apart wall means defining a confinedinsulating space.

FIGURE 2 shows an apparatus that is suitable for producing the heatinsulating material of this invention. At 6 is shown a supply roll offiberglass paper. This paper is led across the driven and guide rollers7 while being passed through a first spraying chamber 8 in which bothsides of it are sprayed by nozzles 9 with an ammoniacal solution ofsilver nitrate, and then through a second spraying chamber 10 in whichboth sides of it are sprayed by nozzles 11 with a reducing solution of'Seignettes salt. The paper is then passed through a drying chamber 12in which it is dried by a current of warm air 13. The finishedinsulating material is then wound upon the roll 14, which may be giventhe same shape as that of the container to which the insulation is to beapplied. Numerals 15a and 15b are drainpipes for removing excess liquidsfrom the spraying chambers.

FIGURE 3 shows a magnified portion (about 12.5X) of the surfaceinsulation made by applying a metal coating onto fiberglass paper. Ascan be seen, there are several superimposed layers of fiberglass paperalternatingly metallized and non-metallized.

FIGURE 3a shows a magnified portion (about 100x of natural size) ofFIGURE 3. The reflecting surfaces consist of a multitude of metallizedfibers with only a spotlike interfiber contact. This very fine divisionof the reflecting surfaces results in an extremely low heat conduction.Since the distances between the metallized fibers are much smaller thanthose between the foils of known insulating materials, the difference intemperature and therewith the heat exchange between adjacentradiationrefiecting layers is smaller, too.

These air permeable metal coated fiberglass layers, in contrast tometallized foils of a homogeneous material, exhibit nearly as highporosities as the aforementioned unmetallized fiberglass layers, for thethickness of the metal coating amounts to approximately one tenth of thethickness of the fiber.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

Consequently, such changes and modifications are properly, equitably,and intended to be, within the full range of equivalence of thefollowing claims.

What is claimed is:

1. Thermal insulation body suitable for low temperature use, comprisinga plurality of films superimposed over one another, each of said filmsconsisting essentially of a non-metallic thermal insulating fibrousmaterial, which fibrous .material is permeable to air and which has aporosity of 88-98%, individual fibers located on at least one of thesurfaces of at least one of said films being coated directly on theiroutward sides with a thin layer of a metal of low emissivity and highreflectivity, said layer having a thickness of 0.01-0.2-10- mm., withthe provision that not all of the fibers of said thermal insulation bodyare completely coated with said thin layer of metal.

2. Thermal insulation as defined by claim 1 wherein the average porediameter in a layer having a thickness of about twice the diameter of asingle of said fibers amounts to about 0.001-O;0l mm.

3. Thermal insulation as defined by claim 1 wherein said fibrousmaterial is predominantly fiberglass-paper having fiber diameters of0.3-10- 10* mm., and wherein said metal is selected from the groupconsisting of gold, silver, copper, and aluminum.

4. A thermal insulation body as defined by claim 1 wherein saidindividual fibers are coated substantially only on their outward sides.

5. A thermal insulation body as defined by claim 1 wherein said thinlayer of metal comprises subdivided reflecting surfaces with point-likecontacts between particles, whereby said thin layer exhibits a lowthermal conductivity as compared to a homogeneous layer of metal.

6. A thermal insulation body as defined by claim 1 wherein said body isnon-combustible.

7. A thermal insulation body as defined by claim 1, comprising at leastmetallized films.

8. A thermal insulation body as defined by claim 1, comprising asandwich-type construction of alternating metallized and non-metallizedfilms, said metallized films being metallized 'on both sides.

9. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 1 in said confined insulating space.

10. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined 'byclaim 2 in said confined insulating space.

11. Thermal insulation as defined by claim 3 wherein all said films arecoated directly on at least one surface with said metal of lowemissivity and high reflectivity.

12. A thermal insulation body as defined by claim 3 wherein saidindividual fibers are coated substantially only on their outward sides.

13. A thermal insulation body as defined by claim3 whereing said thinlayer 'of metal comprises subdivided reflecting surfaces with point-likecontacts between particles, whereby said thin layer exhibits a lowthermal conductivity as compared to a homogeneous layer of metal.

14. A thermal insulation body as defined by claim 3, comprising at least100 metallized films.

'15. A thermal insulation body as defined by claim 3,

comprising a sandwich-type construction of alternating metallized andnon-metallized films, said metallized films being metallized on bothsides.

16. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 3 in said confined insulating space.

17. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvementwhichcomprises the employment of a thermal insulation body as defined byclaim 11 in said confined insulating space.

18. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 4 in said confined insulating space.

19. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 5 in said confined insulating space.

20. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 6 in said confined insulating space.

21. A thermal insulation body as defined by claim 12 wherein said thinlayer of metal comprises subdivided refleeting surfaces with point-likecontacts between particles, whereby said thin layer exhibits a lowthermal conductivity as compared to a homogeneous layer of metal.

22. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 12 in said confined insulating space.

23. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 13 in said confined insulating space.

24. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 21 in said confined insulating space.

25. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 7 in said confined insulating space.

26. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 14 in said confined insulating space.

27. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises the employment of a thermal insulation body as defined byclaim 8 in said confined insulating space.

28. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below at-.

mospheric pressure, the improvement which comprises the employment of athermal insulation body as defined by claim 15 in said confinedinsulating space.

29. A film consisting essentially of a non-metallic thermal-insulatingfibrous material, which fibrous material is permeable to air and whichhas a porosity of 88-98%, individual fibers located on at least one ofthe surfaces of said film being coated directly on their outward sideswith a thin layer of a metal of low emissivity and high reflectivity,said layer having a thickness of 0.010.2 10 mm., with the provision thatnot all of the fibers of said film are completely coated with said thinlayer of metal.

30. A film as defined by claim 29 wherein said fibrous material ispredominantly fiberglass-paper having fiber diameters of 0.310 10* mm.,and wherein said metal is selected from the group consisting of gold,silver, copper, and aluminum.

31. A film as defined by claim 29 wherein said thin layer of metalcomprises subdivided reflecting surfaces with point-like contactsbetween particles, whereby said thin layer exhibits a low thermalconductivity as compared to a homogeneous layer of metal.

32. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises employing as said thermal insulation, a film as defined byclaim 29.

33. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprises employing as said thermal insulation, a film as defined byclaim 30.

34. In an apparatus having spaced-apart wall means defining a confinedinsulating space, said space being at least partially filled withthermal insulation at below atmospheric pressure, the improvement whichcomprising employing as said thermal insulation, a film as defined byclaim 31.

References Cited UNITED STATES PATENTS 2,357,851 9/1944 Scheyer 117-1602,616,165 11/1952 Brennan 117-107 2,630,620 3/1953 Rand 117-1602,731,046 1/1956 Bachner 161-216 2,814,162 11/1957 Toulmin 117-1262,822,509 2/1958 Harvey 117-160 2,919,970 1/1960 Russell 117-1262,921,864 1/1960 Heberlein et al 117-107 2,951,771 9/1960 Butler 117-1263,009,601 11/1961 Matsch 220-9 3,241,702 3/1966 Navikas 220-9 THERON E.CONDON, Primary Examiner.

JAMES R. GARRETT, Examiner.

1. THERMAL INSULATION BODY SUITABLE FOR LOW TEMPERATURE USE, COMPRISING A PLURALITY OF FILMS SUPERIMPOSED OVER ONE ANOTHER, EACH OF SAID FILMS CONSISTING ESSENTIALLY OF A NON-METALLIC THERMAL INSULATING FIBROUS MATERIAL, WHICH FIBROUS MATERIAL IS PERMEABLE TO AIR AND WHICH HAS A POROSITY OF 88-98%, INDIVIDUAL FIBERS LOCATED ON AT LEAST ONE OF THE SURFACES OF AT LEAST ONE OF SAID FILMS BEING COATED DIRECTLY ON THEIR OUTWARD SIDES WITH A THIN LAYER OF A METAL OF LOW EMISSIVITY AND HIGH REFLECTIVITY, SAID LAYER HAVING A THICKNESS OF 0.01-0.2$10**-3 MM., WITH THE PROVISION THAT NOT ALL OF THE FIBERS OF SAID THERMAL INSULATION BODY ARE COMPLETELY COATED WITH SAID THIN LAYER OF METAL. 